The contamination of water with organics, both toxic and non-toxic, has been an ever increasing problem. For example, many industrial processes give rise to waste water streams having contaminating organics therein. Generally, such streams should be treated for the removal of the organics, prior to their discharge into treatment works, lakes, rivers, groundwater supplies, etc. Also, dump sites for organic materials may leak into local groundwater supplies. When this occurs, the groundwater often must be pumped and treated, to prevent the spread of contaminants from the area local to the dump site, by means of the groundwater system.
As suggested previously, the contaminating organics may be either toxic or non-toxic. Both can cause problems. However, non-toxic contaminants generally provide only cosmetic problems, i.e. unpleasant smell, turbidity, color, etc. Toxic compounds may pose an actual health hazard to humans, animals, and/or plants. In either case, it is desirable to remove the organics from the contaminated water, at least to some, reasonable, extent.
Three general classes of methods for removing contaminating organics from water have been developed. These are chemical treatments, biological treatments and physical treatments. Chemical treatments generally involve the introduction of a strong oxidizing agent into the wastewater stream. The contaminating organics are, as a result, partially or fully oxidized to carbon dioxide and water. Examples of oxidizing agents include ozone, chlorine dioxide and hydrogen peroxide.
While in some instances chemical purifications may be desirable, in many they pose problems. First, hazardous chemicals are required. Secondly, they can be relatively expensive. Thirdly, on a large scale, oxidation processes may be relatively slow, unless the oxidant is used in very large amounts.
Physical treatments are also known. These include, for example, carbon adsorption and air stripping. Such methods can be effective in some applications, however they are non-destructive of the toxic material, and thus disposal problems remain.
Biological treatments have been used in a wide variety of applications. Generally, the treatments involve contacting wastewater with a consortium (community) of microorganisms that utilize the dissolved organics as nutrients. In many applications, biological treatments have been difficult to develop, in-part because the contaminants to be removed, especially if highly toxic, have an adverse effect on the viability of many microorganisms.
A common reactor design employed in biological treatments is the mixed tank. For such systems, wastewater is fed to a tank, and aggregates or flocs of microorganisms are suspended in the water. With agitation the microorganisms and water are brought into intimate contact, and the microorganisms act on the organics to remove same from the water. The purified exit stream from the mixed tank generally still contains a suspension of microbial flocs, which are subsequently separated and returned to the treatment tank.
It is noted that the mixed tank reactor design is the basis for many of those activated sludge processes that are used in municipal wastewater treatment plants.
Another method for biological treatment, is to immobilize the microbial consortium in a reactor. The wastewater stream is then passed through the reactor, and the organics are removed. An example of this type of system is one generally referred to as a "trickling filter", in which a film of biomass is developed on a solid support such as rock, wood lath, or plastic packing. The waste stream trickles through the support, bringing the organics into contact with a microbes. Another example is the rotating biological contactor, (RBC), in which biomass laden discs are rotated in a trough, through which the waste stream is directed.
The trickling filter and the RBC are both examples of "fixed-film" biological reactors; that is, the active organisms are contained in an immobile film, which covers a solid support.
A variety of such systems have been developed. In general, for any system to be highly effective, the following concerns must be addressed:
1. First, there is the problem of regulating biomass growth. In some systems, the biomass will feed on the organics sufficiently, so that the fixed biomass will increase substantially. In a trickling filter, an increase in biomass may lead to a plugging of the filter. For an RBC, increase in biomass may inhibit rotational operation of the disc.
2. As previously suggested, it may be desirable to utilize a methodology of treatment including numerous different types of microorganisms in stages. Different stages of microorganisms may require a variety of treatment conditions, for effect. For example, the microorganisms of some stages may be anaerobic, whereas for others they are aerobic. Different temperature and/or nutrient needs may also be present. Also, microorganisms may be needed in one step of the process in order to remove substances toxic to microorganisms used in a later step in the process.
3. For a system to be commercially successful, it must be relatively efficient. It will be understood that very large volumes of water may be need to be treated, for the removal of organics. The water must be fed into, and removed from, the treatment facility. Preferably this is done with relatively low energy demands. Otherwise, the cost of running the plants may make the treatment process economically undesirable, even if the process is superior to others in terms of quality of clean water removed. More specifically, it must be noted that the product of wastewater cleaning is basically clean water, a resource which has relatively little commercial value in and of itself. The by-products, typically biomass waste, and carbon dioxide, also have little or no commercial value.
4. In some instances it may be necessary to set-up wastewater treatment facilities in a field, to handle contaminated water at remote locations. It would be preferred to have a system which is either readily portable, or at least is relatively inexpensive to set-up and take down.
5. In many instances, some of the contaminants in the water, or by-products from the biodegradation, are relatively volatile. It would be preferred to have a purification system wherein release of volatiles or the environment may be controlled, if desired.
6. Finally, if the water to be purified contains toxic materials, the arrangement must be adaptable to handle those materials. That is, materials potentially harmful to the microbial consortium in the reactor must be handlable.
It will be understood that the above list is not exhaustive, rather it generally represents major factors and concerns to be addressed by any effective wastewater purification system, especially those utilizing biological treatments. In general, there has been a need for the development of improved systems and methods, whereby these concerns are conveniently addressed preferably with everincreasing efficiency.
It is an object to the present invention to provide an arrangement for achieving purification of water contaminated with organics, in a manner which effectively addresses some or all of the above listed concerns. It is also an object of the present invention to provide a method whereby these concerns can be readily addressed, in a preferred manner. Other objects and advantages of the present invention will become apparent from the following descriptions, taken in connection with the accompanied drawings, wherein are set forth by way of illustration and examples certain embodiments of the present invention.